05000348/LER-2016-008

LER-2016-008, Manual Reactor Trip Due to Generator Voltage Swings

Joseph M. Farley Nuclear Plant
Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(A), System Actuation
3482016008R00 - NRC Website

LER 16-008-00 for Farley, Unit 1, Regarding Manual Reactor Trip Due to Generator Voltage Swings

ML17023A278
Person / Time
Site:	Farley
Issue date:	01/23/2017
From:	Madison D R Southern Nuclear Operating Co
To:	Document Control Desk, Office of New Reactors
References
NL-17-0005 LER 16-008-00
Download: ML17023A278 (6)

Report °d lessons learned are incomoraled Into the itensirm process and led back to industry Send comments regarding burden estimate to the FOIA, Privacy and Intim riaten Collections Branch (T-5 FS3).Nuclear Regulatory Commission. Washington, °l0555.0001. or by 'Memel e

• mall to Infocollects.Resourceenrc.gov an; to the Desk Officer.ce ol In and Regulaloty Alla is. NEOB-10202, 1315040104), Office of M, nagement and Budget Wash ngton. DC 20S03. 11 3 means used to impose an Inimmation collection does not display a currently valid OMB control number. the NRC may not conduct or sponsor, and a person is not required to respond to, the Information collection Joseph M. Farley Nuclear Plant, Unit 1 05000- 348

A. PLANT AND SYSTEM IDENTIFICATION

Westinghouse - Pressurized Water Reactor

B. DESCRIPTION OF EVENT

On 11/26/16 at 2357 while operating at 100 percent reactor power it was discovered that the Unit 1 main generator [GEN] was experiencing swings in voltage, amps, megawatts, megavars, and speed. The utility's control center assured the control room that the disturbance was emanating from plant Farley.

The Power System Stabilizer (PSS) ERG] for the main generator was showing indications of the swings and was in alarm. At 0026 on 11/27/16 the unit was manually tripped to protect the generator from potential damage. All control rods fully inserted.

The voltage isolation transducer [TD] takes input from the system and uses this signal as an input to the exciter voltage regulator. Review of video taken during the event showed that the gage that reads the output of this isolation transducer was reading zero during the event instead of tracking properly. This was not repeated during troubleshooting, and an intermittent failure of the component was determined to be the cause of the voltage and load swings.

A valid AFW actuation signal started the 1 A and 1B Motor Driven AFW (MDAFW) [BA] system and the Turbine Driven AFW system (TDAFW) [BA] at 0026. At 0037, steam generator [SG] levels were above the TDAFW actuation setpoint and the pump was secured. AFW flow was maintained using MDAFW [BA] to ensure an adequate heat sink per plant procedures, but the SG levels decreased to the TDAFW actuation setpoint at 0041. This was a valid actuation signal and the TDAFW system started a second time. This second start was attributed to TDAFW having been secured with little margin in steam generator narrow range levels in an effort to minimize reactor coolant system [AB] cool down and prevent manual closure of main steam isolation valves [ISV]. The TDAFW system was secured a second time at 0047.

C. UNIT STATUS AT TIME OF EVENT

Mode 1, 100 percent power

D. CAUSE OF EVENT

The cause of the voltage and load swings was an intermittent failure of the voltage isolation transducer.

E. REPORTABILITY ANALYSIS AND SAFETY ASSESSMENT

This event is reportable as required by 10 CFR 50.73(a)(2)(iv)(A) due to a manual actuation of the reactor protection system and automatic actuation of the AFW system. The reactor was shut down at 0026 and entered Mode 3. There was no loss of safety function and no radioactive release associated with this event. All required safety systems were available and responded as expected. There were no actual consequences detrimental to the health and safety of the public and the event is considered to be of very low safety significance.

Reported lessons learned are incorporated into the licensing process and led ba. k to industry Send comments regarding burden estimate to the MIA, Privacy and Informal on Collect ens Bran, h (-1.5 F53), U.S Nuclear Regulatory Commission. Washington DC 20555-0001, Or by Internet e-mail to Inlocollects Resourceenrc.gov. and to the Desk Officer, Office of Into and Regulatory Atlas, NE08-10202 (3150.0104 . 011 ce of Management and Budget Washington, DC 20503 II a means used to Impose an information collection does no du play a currently valid OMB control number, the NFU; may not conduct or sponsor, an a person L not required to respond to, the Information collection.

Joseph M. Farley Nuclear Plant, Unit 1 05000- 348

F. CORRECTIVE ACTION

The voltage isolation transducer was replaced prior to the plant restarting. The transducer module is being sent off for failure analysis to confirm the cause of this failure.

G. ADDITIONAL INFORMATION

1) Previous Similar Events: No other similar previous events have been reported.

2) Commitment Information: This report does not create any licensing commitments